There are many theories about the causes of ovarian cancer. Some of them came from looking at the things that change the risk of ovarian cancer. For example, pregnancy and taking birth control pills both lower the risk of ovarian cancer. Since both of these things reduce the number of times the ovary releases an egg, some researchers think that there may be a link between the release of eggs and the risk of getting ovarian cancer.

Also, we know that women who have had their tubes tied or who have had a hysterectomy have a lower risk of ovarian cancer. One theory to explain this is that some cancer-causing substances may enter the body through the vagina and pass through the uterus and fallopian tubes to reach the ovaries. This would explain the effect of removing the uterus or blocking the fallopian tubes on ovarian cancer risk.

Another theory is that male hormones (androgens) can cause ovarian cancer.

While we do not yet know the exact causes ovarian cancer, we do know some of the risk factors involved. A risk factor is something that changes a person’s chance of getting a disease. Different cancers have different risk factors. Some risk factors, such as smoking, can be controlled. Others, like a person’s age or race, can’t be changed.

But risk factors don’t tell us everything. Having a risk factor, or even several risk factors, does not mean that you will get the disease. And many people who get the disease may not have had any known risk factors. Even if a woman with ovarian cancer has a risk factor, it is very hard to know how much that risk factor may have contributed to the cancer.

Risk factors for ovarian cancer

Some of the risk factors for the most common type of ovarian cancer (epithelial ovarian cancer) are listed below.

Age: Most ovarian cancers happen after change of life (menopause). Half of all these cancers are found in women over the age of 63.

Obesity: It appears that obese women have a higher risk of getting ovarian cancer. One ACS study found a higher rate of death from ovarian cancer in women who were overweight. The risk went up by 50% in the heaviest women.

Having children: A woman who has had children has a lower risk of ovarian cancer than women who have no children. The risk gets even lower with each pregnancy. Breast feeding may lower the risk even further. Using birth control pills (“the pill’) also lowers the risk of ovarian cancer.

Female surgery: Having your “tubes tied” (tubal ligation) may reduce the chance of developing ovarian cancer. A hysterectomy (removal of the uterus without removing the ovaries) also seems to reduce the risk of getting ovarian cancer.

Fertility drugs: Some studies have found that use of the fertility drug Clomid® for longer than 1 year, especially if no pregnancy took place, may increase the risk of LMP tumors. But not having children also increases the risk, even without the use of fertility drugs. Research in this area is now going on. If you are taking this drug, you should talk to your doctor about the possible risks.

Male hormones: Androgens are male hormones. A recent study found a link between the drug danazol (used to treat endometriosis) and an increased risk of ovarian cancer. Further studies are planned to look at this.

Estrogen replacement therapy and hormone replacement therapy: Some recent studies suggest women using estrogens after change of life have an increased risk of developing ovarian cancer. The risk seems to be higher in women taking estrogen alone (without progesterone) for many years (at least 5 or 10). The increased risk is less certain for women taking both estrogen and progesterone.

Family history of ovarian cancer, breast cancer, or colorectal cancer: Ovarian cancer can run in families. Your ovarian cancer risk is higher if your mother, sister, or daughter has or had ovarian cancer. The younger your family member was when she got ovarian cancer, the higher your risk. The risk also gets higher the more relatives you have with ovarian cancer. Increased risk for ovarian cancer does not have to come from your mother’s side of the family – it can also come from your father’s side.

Having a family member with breast cancer can increase your risk of ovarian cancer. And women who have colon cancer in their families may have a higher risk of developing ovarian cancer.

About 1 in 10 cases of ovarian cancers are linked to gene changes that can be found with certain tests. These changes are also linked to an increased risk of breast and colorectal cancer. Please see the section on prevention to learn about genetic counseling and testing.

Breast cancer: Women who have had breast cancer also have a higher risk of ovarian cancer.

Talcum powder: Some studies have shown a slight increase in risk of ovarian cancer among women who used talcum powder on the genital area. Asbestos in the powder may explain the link. But these products have been free of asbestos for more than 20 years. Proving the safety of newer products will require further follow-up studies.

Diet: A recent study of women who followed a low-fat diet for at least 4 years showed a lower risk of ovarian cancer. Some studies have shown a reduced rate of ovarian cancer in women who ate a diet high in vegetables, but other studies disagree.

Smoking and alcohol use: Some studies have found an increased risk for one type of ovarian cancer (mutinous).